1. Field of the Invention
This invention relates to drums made of synthetic resins and more particularly to such plastic drums that can be sealed by a gasketless lid or cover so as to prevent air and water vapor from entering the closed drum.
2. Brief Description of the Prior Art
Drums and similar containers made from synthetic resin have come to be used extensively in storage and shipment of granular materials of all types. Such drums are inexpensive, durable, and corrosion resistant. Open-head drums of this type are generally provided with a circular rim or chime at the open upper end. Such drums are closed with a separate cover or lid that is clamped to the chime of the drum. Conventionally, the lid is provided with a gasket that engages the chime to form a seal. The gasket is typically made of a synthetic resin that is somewhat softer than the body of the drum and the lid in order to conform exactly to the upper edge of the chime.
Such drums having gasketed lids are generally satisfactory for storage and transportation of materials. However the use of gaskets to form a seal between the lid and the chime has certain drawbacks. The separate manufacture of a gasket requires an assembly step in the manufacture of the drum cover, which increases the cost of manufacture. In some cases the relatively soft gasket material may permit the passage of water vapor through the seal, as well as contaminate the product packaged if it becomes torn or abraded.
Accordingly, a need has continued to exist for a drum lid or cover that does not suffer from the disadvantages of a gasketed drum lid.